The R Project SVN R

% File src/library/base/man/Sys.which.Rd

% Part of the R package, http://www.R-project.org

% Copyright 2007-12 R Core Team

% Distributed under GPL 2 or later

\name{Sys.which}

\alias{Sys.which}

\title{Find Full Paths to Executables}

\description{

  This is an interface to the system command \code{which}, or to an

  emulation on Windows.

}

\usage{

Sys.which(names)

}

\arguments{

  \item{names}{Character vector of names or paths of possible executables.}

}

\details{

  The system command \command{which} reports on the full path names of

  an executable (including an executable script) as would be executed by

  a shell, accepting either absolute paths or looking on the path.

  On Windows an \sQuote{executable} is a file with extension

  \file{.exe}, \file{.com}, \file{.cmd} or \file{.bat}.  Such files need

  not actually be executable, but they are what \code{\link{system}}

  tries.

  On a Unix-alike the full path to \code{which} (usually

  \file{/usr/bin/which}) is found when \R is installed.

}

\value{

  A character vector of the same length as \code{names}, named by

  \code{names}.  The elements are either the full path to the

  executable  or some indication that no executable of that name was

  found.  Typically the indication is \code{""}, but this does depend on

  the OS (and the known exceptions are changed to \code{""}).  Missing

  values in \code{names} have missing return values (as from \R 3.0.0).

  On Windows the paths will be short paths (8+3 components, no spaces)

  with \code{\\} as the path delimiter.

}

\note{

  Except on Windows this calls the system command \command{which}: since

  that is not part of e.g. the POSIX standards, exactly what it does is

  OS-dependent.  It will usually do tilde-expansion and it may make use

  of \command{csh} aliases.

  In \R 2.x.y, arguments containing spaces or other metacharacters

  needed to be escaped as they would be for a shell: for example Windows

  paths containing spaces needed to be enclosed in double quotes.

}

\examples{

## the first two are likely to exist everywhere

## texi2dvi exists on most Unix-alikes and under MiKTeX

Sys.which(c("ftp", "ping", "texi2dvi", "this-does-not-exist"))

}

\keyword{ utilities }